Method of manufacturing insulating firebrick



Patented May 20, 1941 2,242,434 FsFI'CiE METHOD OF MANUFACTURINGINSULATING Fl-REBRICK Charles L. Norton, Jr., New York, N. Y., assignorto The'Ba'bcock & Wilcox Company, Newark, N. J., a corporation :of NewJersey NoDrawing. Application February 27, 1937, Serial No. 128,162

Claims.

This invention is an improvement inthear't of light weight, highstrength, permeable, cellular, ceramic products and their manufacture,particularly relating to those of a character adapted for use as heatinsulator-s and also having good acoustic properties whereby noises, forinstance, accompanying firing of and flame propagation in a furnace maybe quieted to a marked degree.

In the manufacture of such ceramic products processes have heretoforebeen proposed, and products have been successfully manufactured bycombining various proportions of argillaceous material, wood or othercombustible or eliminative particles and water, the solid materialsfirst being mixed dry, water then added and the whole being mixed to anextent which results in air bubbles being liberally interspersed; thenmolding the mixture, drying the molded shapes, and finally firing thedried shapes to burn out the combustible or remove the eliminableparticles of the mixture under such conditions as avoid disintegrationof the shapes and preserve the cellular structure created by theentrained air bubbles and elimination :of such particles while, at thesame time, rendering the product porous.

In order to facilitate handling of the molded shapes priorto burning,such mixtures as above outlined and treated have also .had added to thema small amount of some hydraulic setting agent such as calcined gypsumor the like.

However, with such mixtures the rate of productionnecessarily has beenslow, due to the fact that in the manufacture of bricks of ordinarysize, such as 4%" x 9" 'x 2 the drying step has been considerednecessaryjin order to remove moisture before burning-the brick shapesbeing dried for a period of 12 hours at a temperature of approximately225 F. This drying step. before burning, has the disadvantage ofrequiring additional expenditure of fuel, and large storage space forunburned shapes in order that an adequate supply of dried shapes maybekept ahead to provide suitable quantities for economically operatinglarge sizekilns, with consequently high overhead charges in themanufacture.

An object of the present invention is to provide a method and a productof the character described wherein the drying step is eliminated.

A further object is a method and a product of the character describedwherein the stability of the mass, after being mixed, is such as toeliminate the usual step of molding, should it be desirable, and permitthe extrusion of the mass through a die and the utilization ofappropriate cutting-off means to sever the extruded strip into brickshapes.

One manner in which the invention has been commercially practiced is toform a dry batch mixture according to the following formula:

. Pounds Plaster of Paris (CaSOUI-IzO) 3'7 4-8 mesh wood sawdust '37Pulverized. Georgia kaolin The foregoing materials for the batch arecommercially dry, that is to say they contain only the normal moisturecontent incident to storage in the air.

These dry materials are paddle mixed in a container for a time "intervalsuch that there is an intimate association of the particles of the mass.

The dry batch 'isthen similarly paddle mixed in another container wherewater is added in sufficient quantity to condition the mix for the stepof forming into shapes. The shapes may be formed by extrusion and wirecutting or by casting to shape, or by casting a slab and wire cutting.

To form -a fiowable castable mixture of the above batch water is usuallyadded in an amount equal to 100% by weight, but atmospheric 'conditions,the type, amount and condition of the starting materials, and thecharacter of forming step to be used dictate and actual relationship ofadded moisture to dry materials.

In forming the above mixture into shapes for standard fire brick unitswhen fired and finally sized, the mixture of fiowable castableconsistency was'cast into molds after dry and wet mixing periods of 30seconds each with a transfer interval of 20 seconds from dry to wetmixer.

In the particular operation referred to molding was accomplished bycasting into mold shapes each of which was 30" x 10 x 5". The slabs thusobtained were then each wire cut to provide nine slugs ready for firing.After casting the filled molds are allowed to set for only a suffi'cientperiod oftime to permit recrystallization of the plaster of Paris.

Instead of wire cutting division plates or partitions may be used in themolds. When extrusion is used two of the required dimensions are fixedby the die head used, whereas the third is obtained by governing therate of extrusion and wire cutting at uniform intervals. Another methodof molding commonly referred to as extruding and which may also be usedis to cast the shapes into a mold form from which they are removed ontooiled shods by push blocks contacting one face of the cast shape whilethe mold and its respective push block are moved relatively to displacethe brick shape. From the foregoing it is apparent that molding orshaping of the wet material is not restricted to any parmethods may beemployed.

After formation of the brick shapes and recrystallization of the plasterof Paris it will be found that while still wet they are, nevertheless,

in condition to be readily transported and placed;

in the kiln.

The wet shapes are placed in the entrance of a; I

perature level than the interior too rapidly and promote uniformity oftemperature penetration with-the result that leeway in kiln regulationis greaterfand there is less opportunity for the development of surfaceand other flaws in the finished shape. I

The water vapor and gases due to distillation of the combustibleparticles are many hundreds of times greater in volume than the originalwater or combustible volume, and escape through minute ruptures of thecellular walls which thus adds porosity to the structure, but suchruptures are so minute in the finished product as to impose considerableresistance to the passage of gases through the ultimate brick. I I

At approximately the stage where carbonization of the combustibleparticles is complete throughout the brick shapes and where there isnofurther danger of uncontrollable combustion of the same adding tothe'temperature of the kiln, the reducing atmosphere is replaced withanoxidizing atmosphere and the temperature elevated over a suitable timeinterval to 2350 F., the carbon particles are thus completelyeliminated,leaving minute voids or cells which by volume constitute better than 70%of the volume of the shape.

The resulting product is a light weight insulating firebrick refractoryto 2200-F., of low thermal conductivity, with unusual stability, whichmay be cut and sized with ordinary wood saws, will receive screws, boltsor nails, and has the property of absorbing sound to a marked degree. Inuse'it effects a substantial saving in industrial furnace operation byreducing both the'timeand fuel, or electric current energy, required toreach thermal equilibrium.

Authenticated tests for thermal conductivity and fusion at thelaboratories of Massachusetts Institute of Technology for brick made inaccordance with the foregoing formula and method are as follows:

An additional advantage incident to wet burning as compared with burningthe shapes after drying is that the volume shrinkage of the dried shapeswhile burning is materially greater; 'It was found that with slugs madefrom the same were burned undried.

The result is that the density of the dried and fired material was asmuch as 16% more than the density of the undried and fired material andthe volume shrinkage of the dried and fired material was nearly twicethat of the volume shrinkage of the undried and fired material; forinstance, in measured samples the volume shrinkage of the undried andfired material was 16.7%,

while that of the dried and fired material was 32.6%, the weight of afinished brick size of the fired undried sample was ,1.98# whereas thatof the dried and fired sample was 2.29#. It is a well known fact thatwith materials of essentially the same composition the thermalconductivity will increase directly with an increase in the weight of agiven volume, thus conclusively demonstrating the superiority of theproduct of this invention over that produced by methods used heretofore.

Additionally contributing to the superiority of the product is the factthat the starting materials do not contain just sufiicient plaster ofParis to cause setting but have an additional.

amount over that required for setting. With amounts as low as isrequired only for setting undue shrinkage in firing is encountered, butgwith the use of as much as 21% of the dry mix, as is the case inapplicants invention, a real advantage is gained for this reason: Thefired shape is rendered more cellular and consequently lighterin weightby the incorporation in the starting materials of enough plaster ofParis and water; the plasterof Paris, on burning the shape, loses all ofits water of combination as well as any that is mechanically present,and also the sulphate radical breaks up, leaving merely CaO to combinewith silica in stable compounds. This loss of water of combination bythe plaster of Paris and the breaking up of the sulphate radical leavesminute voids or cells in large numbers in addition to those due toaeration and burning out of wood particles, for instance a pound of setplaster of Paris dead burned is reduced to .3 of a pound (approx). Inthe burned shape of the formula incorporated herein each slug originallycontains approximately .8 lb. of plaster of Paris which, after firing isreduced in weight to approximately .22 1b., the loss in weight resultingin additional cells. Inthe claims, the terms molded and molding areintended to generically cover the various methods of forming the desiredshapes described herein and equivalent methods; the term burningtemperature is used to define kiln temperature conditions sufficient toheat the surface of the brick within one (1) hour of being inserted to atemperature several hundred F. higher than the maximum ebricktemperature attained heretofore during ordinary drying operations.

Iclaim- 1. The method of making a ceramic product which comprises mixingargillaceous material and a hydraulic setting agent with water toflowable consistency, forming the shapes before setting occurs, and'thensubjecting the shapes to a burning temperature While they still retainsubstantially all of the water of the mixture.

'2. The method of making a refractory product which comprises intimatelymixing refractory material, eliminable particles, a hydraulic settingagent, and waterto flowable formable consistency, forming the shapesbefore setting occurs, and subjecting the shapes to a burningtemperature while the mixture still retains substantially all of itswater and whereby eliminable particles disappear to leave a cellularstructure.

3. The method of making a ceramic'product which comprises intimatelymixing argillaceous material, combustible particles, a hydraulic settingagent, and water to flowable formable conable mass, forming into shapesprior to recrystalization of the plaster of Paris, and subjecting theshapes to a burning temperature while the mixture still retainssubstantially all of its water.

5. The method of making a ceramic product which comprises intimately drymixing pulveriaed kaolin, wood flour and plaster of Paris, adding waterwhile mixing to form a flowable formable mass, forming into shapes priorto recrystallization, subjecting the shapes, while the mixture stillretains substantially all of its water, to a burning temperature in areducing atmosphere to carbonize the wood flour, and then burning at ahigher temperature in an oxidizing atmosphere whereby the carbonparticles are eliminated.

6. The method of making a ceramic product which comprises intimately drymixing plaster of Paris, wood flour, and Georgia kaolin in the ratio of37 pounds of plaster of Paris, 37 pounds of Wood flour and 100 pounds ofGeorgia kaolin,

all in pulverized form, adding 100 per cent water while mixing to form aflowable castable mass, molding shapes therefrom prior torecrystallization of the plaster of Paris, firing the shapes at aburning temperature in a reducing atmosphere while the mixture, stillretains substantially all of its water and immediately followingrecrystallization of the plaster of Paris to completely carbonize thewood flour, and then firing at a higher temperature in an oxidizingatmosphere.

'7. The method of making a burnt cellular ceramic product whichcomprises forming a flowable moldable mixture of argillaceous material,gypsum and water, with an excess of gypsum over that required forsuificiently strengthening the mixture when molded into shapes to permithandling, molding the mixture into shapes, and then subjecting theshaped mixture while it still retains substantially all of its water toa temperature sufiicient to break up the sulphate radical of the gypsumwhereby voids are produced throughout the mass.

8. The method of making light-weight refractory products which comprisesforming a flowable moldable mixture of refractory material, a hydrauliccement, and water, molding the mixture intoshapes, and subjecting themolded shapes when set and while retaining substantially all of thewater present therein when molded to a burning temperature.

9. The method of making light-weight refractory products from moldedshapes containing a mixture of refractory material, combustibleparticles, and a substantial amount of water which comprises subjectingthe molded shapes while containing an amount of water equal to at least30% of the weight of the dry materials included therein to a burningtemperature.

10. The method of making light-weight refractory products from moldedshapes made from a flowable mixture of refractory material, a hydrauiiccement, and a substantial amount of water which comprises subjecting themolded shapes while containing substantially all of the water. presenttherein after being molded to a burning temperature. v

11. The method of burning molded shapes made from a fiowable mixture ofrefractory material, a hydraulic cement, combustible particles, and asubstantial amount of water to form lightweight porous refractoryproducts which comprises subjecting the molded shapes while containingsubstantially all of the water present therein after being molded to aburning temperature, and rapidly heating the same to a temperature abovethe ignition temperature of the combustible particles.

12. In the manufacture of refractory products from an argillaceous basematerial normally having a high shrinkage when fired, the method ofmaking such products with a minimum firing shrinkage which comprisesmixing a hydraulic setting agent and a substantial amount of water withthe argillaceous material to a flowable consistency, molding the mixtureinto the desired .final shapes, and subjecting the molded shapes whensetand while containing substantially all of the water present thereinwhen molded to a continuous firing cycle in which the molded shapes arerapidly heated to a temperature substantially above 1600 F.

13. The method of making light-weight insulating brick which comprisesmolding a flowable mixture of pulverized kaolin, combustible particles,a hydraulic cement, and water into the de sired brick shapes, andsubjecting the molded shapes when set and while retaining substantiallyall of the water present therein when mold- ,ed to a continuous firingcycle in which the molded shapes are rapidly heated to a temperatureabove 1000 F.

14. The method of making light-weight insulating brick which comprisesmolding an aerated flowable mixture of pulverized kaolin, combustibleparticles, a hydraulic cement, and water into the desired brick shapes,and subjecting the molded shapes when set and while retainingsubstantially all of the water present therein when molded to acontinuous firing cycle in which the molded shapes are rapidly heated toa temperature above 1000 F. in a reducing atmosphere and subsequentlyheated at substantially higher temperatures in an oxidizing atmosphere.

15. The method of making lightweight porous refractory products whichcomprises molding into shapes a flowable mixture of refractory material,water and an amount of plaster of Paris substantially in excess of thamount required when set to sufliciently strengthen the molded shapes topermit handling thereof, and then subjecting the molded shapes when setand while re taining substantially all of the water present therein whenmolded to a temperature sufficient to break up the sulphate radical ofthe plaster of Paris.

CHARLES L. NORTON, JR.

